OTRC: Kate Middleton is pregnant: Duchess of Cambridge, Prince William expecting first child

Kate Middleton, aka Catherine, Duchess of Cambridge, and husband Prince William of the United Kingdom are expecting their first child.

The news was announced on Monday, December 3, by St James's Palace, who added that the duchess was admitted that afternoon to a London hospital to treat Hyperemesis Gravidarum, also known as morning sickness. Symptoms include severe, persistent nausea and lightheadedness or fainting, according to the U.S. National Library of Medicine. William joined his wife at the hospital, the UK Press Association reported.

"Their Royal Highnesses The Duke and Duchess of Cambridge are very pleased to announce that The Duchess of Cambridge is expecting a baby. As the pregnancy is in its very early stages, Her Royal Highness is expected to stay in hospital for several days and will require a period of rest thereafter," palace officials said in a statement.

They did not disclose when Kate is due to give birth. Pregnant women usually experience symptoms of morning sickness when they are between about two and 12 weeks along.

A palace source told ABC News that Kate is not yet 12 weeks pregnant and that given her hospitalization, she and her husband had made the "difficult decision to be fully open about the pregnancy from this stage."

Kate and William married in a televised ceremony in April 2011. Their child could potentially become the heir to the British throne. The prince, the grandson of Queen Elizabeth II, is second in line.

"The Queen, The Duke of Edinburgh, The Prince of Wales, The Duchess of Cornwall and Prince Harry and members of both families are delighted with the news," palace officials said in the pregnancy announcement, referring to the British monarch and her husband Philip, Charles and his wife and William's stepmother Camilla and the prince's younger brother Harry.

She and William were on Monday also congratulated by the likes of UK Prime Minister David Cameron, who told reporters he is "delighted for them" and is "sure they will make absolutely brilliant parents" and U.S. President Barack Obama and First Lady Michelle Obama.

"I know they both feel that having a child is one of the most wonderful parts of their lives, so I'm sure that will be the same for the Duke and Duchess of Cambridge," White House Press Secretary Jay Carney told reporters.

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